The present invention relates to a stern tube seal device which provides a seal about a rotatable shaft.
A stern tube seal device heretofore known includes a plurality of lip seals fixed to the inner periphery of of an opening in an annular case member arranged at the outer periphery of a shaft. The lip seal located externally (on the sea water side) is arranged to face towards the outside of the ship (sea water), and the lip seal located internally (on the machine side) is arranged to face towards the inside of the ship (lubricating oil). Leaking of sea water into the ship and leaking of lubricating oil outside the ship are prevented by sealing and sliding rotation of the shaft with respect to these lip seals. According to the above-described prior art device, the aforesaid external lip seal receives all the sea water pressure and the sliding load thereof with the shaft increases thereby resulting in early wearing. In addition, a second seal is not present with respect to leakage of lubricating oil and the leaked oil is not recovered, thus resulting in a danger in that the lubricating oil will flow outside the ship to contaminate the sea.